diff --git a/packages/babel-helper-builder-react-jsx-experimental/src/index.js b/packages/babel-helper-builder-react-jsx-experimental/src/index.js
index 2e163dc65112..2f196d8e2fde 100644
--- a/packages/babel-helper-builder-react-jsx-experimental/src/index.js
+++ b/packages/babel-helper-builder-react-jsx-experimental/src/index.js
@@ -138,136 +138,134 @@ You can set \`throwIfNamespace: false\` to bypass this warning.`,
 
     Program: {
       enter(path, state) {
-        if (hasJSX(path)) {
-          const { file } = state;
-          let runtime = RUNTIME_DEFAULT;
-
-          // For jsx mode
-          let source = IMPORT_SOURCE_DEFAULT;
-          let sourceSet = !!options.importSource;
-
-          // For createElement mode
-          let pragma = PRAGMA_DEFAULT;
-          let pragmaFrag = PRAGMA_FRAG_DEFAULT;
-          let pragmaSet = !!options.pragma;
-          let pragmaFragSet = !!options.pragmaFrag;
-
-          if (file.ast.comments) {
-            for (const comment of (file.ast.comments: Array<Object>)) {
-              const sourceMatches = JSX_SOURCE_ANNOTATION_REGEX.exec(
-                comment.value,
-              );
-              if (sourceMatches) {
-                source = sourceMatches[1];
-                sourceSet = true;
-              }
-
-              const runtimeMatches = JSX_RUNTIME_ANNOTATION_REGEX.exec(
-                comment.value,
-              );
-              if (runtimeMatches) {
-                runtime = runtimeMatches[1];
-              }
-
-              const jsxMatches = JSX_ANNOTATION_REGEX.exec(comment.value);
-              if (jsxMatches) {
-                pragma = jsxMatches[1];
-                pragmaSet = true;
-              }
-              const jsxFragMatches = JSX_FRAG_ANNOTATION_REGEX.exec(
-                comment.value,
-              );
-              if (jsxFragMatches) {
-                pragmaFrag = jsxFragMatches[1];
-                pragmaFragSet = true;
-              }
+        const { file } = state;
+        let runtime = RUNTIME_DEFAULT;
+
+        // For jsx mode
+        let source = IMPORT_SOURCE_DEFAULT;
+        let sourceSet = !!options.importSource;
+
+        // For createElement mode
+        let pragma = PRAGMA_DEFAULT;
+        let pragmaFrag = PRAGMA_FRAG_DEFAULT;
+        let pragmaSet = !!options.pragma;
+        let pragmaFragSet = !!options.pragmaFrag;
+
+        if (file.ast.comments) {
+          for (const comment of (file.ast.comments: Array<Object>)) {
+            const sourceMatches = JSX_SOURCE_ANNOTATION_REGEX.exec(
+              comment.value,
+            );
+            if (sourceMatches) {
+              source = sourceMatches[1];
+              sourceSet = true;
             }
-          }
 
-          state.set("@babel/plugin-react-jsx/runtime", runtime);
-          if (runtime === "classic") {
-            if (sourceSet) {
-              throw path.buildCodeFrameError(
-                `importSource cannot be set when runtime is classic.`,
-              );
-            }
-            state.set(
-              "@babel/plugin-react-jsx/createElementIdentifier",
-              createIdentifierParser(pragma),
+            const runtimeMatches = JSX_RUNTIME_ANNOTATION_REGEX.exec(
+              comment.value,
             );
-            state.set(
-              "@babel/plugin-react-jsx/jsxFragIdentifier",
-              createIdentifierParser(pragmaFrag),
-            );
-            state.set("@babel/plugin-react-jsx/usedFragment", false);
-            state.set(
-              "@babel/plugin-react-jsx/pragmaSet",
-              pragma !== DEFAULT.pragma,
-            );
-            state.set(
-              "@babel/plugin-react-jsx/pragmaFragSet",
-              pragmaFrag !== DEFAULT.pragmaFrag,
+            if (runtimeMatches) {
+              runtime = runtimeMatches[1];
+            }
+
+            const jsxMatches = JSX_ANNOTATION_REGEX.exec(comment.value);
+            if (jsxMatches) {
+              pragma = jsxMatches[1];
+              pragmaSet = true;
+            }
+            const jsxFragMatches = JSX_FRAG_ANNOTATION_REGEX.exec(
+              comment.value,
             );
-          } else if (runtime === "automatic") {
-            if (pragmaSet || pragmaFragSet) {
-              throw path.buildCodeFrameError(
-                `pragma and pragmaFrag cannot be set when runtime is automatic.`,
-              );
+            if (jsxFragMatches) {
+              pragmaFrag = jsxFragMatches[1];
+              pragmaFragSet = true;
             }
+          }
+        }
 
-            const importName = addAutoImports(path, {
-              ...state.opts,
-              source,
-            });
-
-            state.set(
-              "@babel/plugin-react-jsx/jsxIdentifier",
-              createIdentifierParser(
-                createIdentifierName(
-                  path,
-                  options.development ? "jsxDEV" : "jsx",
-                  importName,
-                ),
-              ),
+        state.set("@babel/plugin-react-jsx/runtime", runtime);
+        if (runtime === "classic") {
+          if (sourceSet) {
+            throw path.buildCodeFrameError(
+              `importSource cannot be set when runtime is classic.`,
             );
-            state.set(
-              "@babel/plugin-react-jsx/jsxStaticIdentifier",
-              createIdentifierParser(
-                createIdentifierName(
-                  path,
-                  options.development ? "jsxDEV" : "jsxs",
-                  importName,
-                ),
-              ),
+          }
+          state.set(
+            "@babel/plugin-react-jsx/createElementIdentifier",
+            createIdentifierParser(pragma),
+          );
+          state.set(
+            "@babel/plugin-react-jsx/jsxFragIdentifier",
+            createIdentifierParser(pragmaFrag),
+          );
+          state.set("@babel/plugin-react-jsx/usedFragment", false);
+          state.set(
+            "@babel/plugin-react-jsx/pragmaSet",
+            pragma !== DEFAULT.pragma,
+          );
+          state.set(
+            "@babel/plugin-react-jsx/pragmaFragSet",
+            pragmaFrag !== DEFAULT.pragmaFrag,
+          );
+        } else if (runtime === "automatic") {
+          if (pragmaSet || pragmaFragSet) {
+            throw path.buildCodeFrameError(
+              `pragma and pragmaFrag cannot be set when runtime is automatic.`,
             );
+          }
 
-            state.set(
-              "@babel/plugin-react-jsx/createElementIdentifier",
-              createIdentifierParser(
-                createIdentifierName(path, "createElement", importName),
+          const importName = addAutoImports(path, {
+            ...state.opts,
+            source,
+          });
+
+          state.set(
+            "@babel/plugin-react-jsx/jsxIdentifier",
+            createIdentifierParser(
+              createIdentifierName(
+                path,
+                options.development ? "jsxDEV" : "jsx",
+                importName,
               ),
-            );
-
-            state.set(
-              "@babel/plugin-react-jsx/jsxFragIdentifier",
-              createIdentifierParser(
-                createIdentifierName(path, "Fragment", importName),
+            ),
+          );
+          state.set(
+            "@babel/plugin-react-jsx/jsxStaticIdentifier",
+            createIdentifierParser(
+              createIdentifierName(
+                path,
+                options.development ? "jsxDEV" : "jsxs",
+                importName,
               ),
-            );
+            ),
+          );
 
-            state.set(
-              "@babel/plugin-react-jsx/importSourceSet",
-              source !== DEFAULT.importSource,
-            );
-          } else {
-            throw path.buildCodeFrameError(
-              `Runtime must be either "classic" or "automatic".`,
-            );
-          }
+          state.set(
+            "@babel/plugin-react-jsx/createElementIdentifier",
+            createIdentifierParser(
+              createIdentifierName(path, "createElement", importName),
+            ),
+          );
 
-          if (options.development) {
-            path.traverse(injectMetaPropertiesVisitor, state);
-          }
+          state.set(
+            "@babel/plugin-react-jsx/jsxFragIdentifier",
+            createIdentifierParser(
+              createIdentifierName(path, "Fragment", importName),
+            ),
+          );
+
+          state.set(
+            "@babel/plugin-react-jsx/importSourceSet",
+            source !== DEFAULT.importSource,
+          );
+        } else {
+          throw path.buildCodeFrameError(
+            `Runtime must be either "classic" or "automatic".`,
+          );
+        }
+
+        if (options.development) {
+          path.traverse(injectMetaPropertiesVisitor, state);
         }
       },
 
@@ -353,18 +351,6 @@ You can set \`throwIfNamespace: false\` to bypass this warning.`,
     return imports;
   }
 
-  function hasJSX(parentPath) {
-    let fileHasJSX = false;
-    parentPath.traverse({
-      "JSXElement|JSXFragment"(path) {
-        fileHasJSX = true;
-        path.stop();
-      },
-    });
-
-    return fileHasJSX;
-  }
-
   function getSource(source, importName) {
     switch (importName) {
       case "Fragment":
diff --git a/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-automatic/input.js b/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-automatic/input.js
new file mode 100644
index 000000000000..8f34f4659447
--- /dev/null
+++ b/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-automatic/input.js
@@ -0,0 +1 @@
+const foo = 2;
diff --git a/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-automatic/options.json b/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-automatic/options.json
new file mode 100644
index 000000000000..b8505036d209
--- /dev/null
+++ b/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-automatic/options.json
@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    ["transform-react-jsx", { "runtime": "automatic" }],
+    "./plugin.js"
+  ]
+}
diff --git a/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-automatic/output.js b/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-automatic/output.js
new file mode 100644
index 000000000000..7a12700836b4
--- /dev/null
+++ b/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-automatic/output.js
@@ -0,0 +1 @@
+const foo = /*#__PURE__*/undefined.jsx("p", {});
diff --git a/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-automatic/plugin.js b/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-automatic/plugin.js
new file mode 100644
index 000000000000..008f85eda2a4
--- /dev/null
+++ b/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-automatic/plugin.js
@@ -0,0 +1,13 @@
+module.exports = ({ types: t }) => ({
+  visitor: {
+    NumericLiteral(path) {
+      path.replaceWith(
+        t.jsxElement(
+          t.jsxOpeningElement(t.jsxIdentifier("p"), []),
+          t.jsxClosingElement(t.jsxIdentifier("p")),
+          []
+        )
+      );
+    }
+  }
+});
diff --git a/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-classic/input.js b/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-classic/input.js
new file mode 100644
index 000000000000..8f34f4659447
--- /dev/null
+++ b/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-classic/input.js
@@ -0,0 +1 @@
+const foo = 2;
diff --git a/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-classic/options.json b/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-classic/options.json
new file mode 100644
index 000000000000..4dba1655893c
--- /dev/null
+++ b/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-classic/options.json
@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    ["transform-react-jsx", { "runtime": "classic" }],
+    "./plugin.js"
+  ]
+}
diff --git a/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-classic/output.js b/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-classic/output.js
new file mode 100644
index 000000000000..b28842cb637a
--- /dev/null
+++ b/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-classic/output.js
@@ -0,0 +1 @@
+const foo = /*#__PURE__*/React.createElement("p", null);
diff --git a/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-classic/plugin.js b/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-classic/plugin.js
new file mode 100644
index 000000000000..008f85eda2a4
--- /dev/null
+++ b/packages/babel-plugin-transform-react-jsx/test/fixtures/regression/issue-12478-classic/plugin.js
@@ -0,0 +1,13 @@
+module.exports = ({ types: t }) => ({
+  visitor: {
+    NumericLiteral(path) {
+      path.replaceWith(
+        t.jsxElement(
+          t.jsxOpeningElement(t.jsxIdentifier("p"), []),
+          t.jsxClosingElement(t.jsxIdentifier("p")),
+          []
+        )
+      );
+    }
+  }
+});